The invention relates to a conductive paste for the electrical industry and also to its use.
Materials of this type are widely used and are needed in numerous applications. For example, the material has particular importance in connection with the sealing of electromagnetically shielded housings in electronic devices which emit electromagnetic radiation or can be disturbed by electromagnetic radiation penetrating from outside. The housings are produced from an electrically conducting material, or from a material coated so as to be electrically conducting, in order to provide EMI (electromagnetic interference) and, respectively, RFI (radio frequency interference) shielding and to improve electromagnetic compatibility (EMC). It is known that the region of the joints at which the parts of the housing are joined can also be given shielding by using gaskets made from an electrically conducting flexible material.
An example of a material of this type is known from U.S. Pat. No. 4,011,360. This known material is based on an elastomer, typically a silicone rubber material, with an admixture of electrically conducting particles. This material polymerizes when exposed to atmospheric moisture at room temperature.
DE 43 19 965 C2 discloses the use of a material of this type for the production of the housings described at the outset. The starting material is extruded as a strand of paste directly in the region of the joint onto one of the parts of the housing, and polymerizes there to form the gasket. This process is also known to the skilled worker as the formed-in-place-gasket process.
Materials of this type with electrically conducting particles are moreover used for forming contact points or contact areas, known as contact pads. They thus take on the function of contact elements.
It is also possible to use thermally conductive particles in order to form what are known as thermal pads. These have the task of dissipating, for example, heat from an electronic component and of passing the same to a cooling element. One of the most important examples of the application is a microprocessor unit in which the heat generated by the processor is to be passed to a cooling carrier exposed to a fan.
Despite their undisputed useful properties, materials of this type based on silicone have some disadvantages.
In this connection a particular problem is that the silicone has the property of emitting gaseous materials with short molecular chains. These constituents condense on (adjacent) metal parts or cold sections of surfaces. The silicone oil deposit insulates the surface (mostly undesirably). For example, it has been observed that a deposit of this type considerably impairs, or destroys, the function of contact relays. Even if the contact is closed mechanically, the deposited silicone oil film can completely prevent electrical contact. Despite the recognized good properties of silicone-containing materials, they have therefore been largely eliminated by the telephone industry.
Another problem is that the silicone oil film drastically impairs the adhesion of the surface. This problem is particularly evident in the motor vehicle industry, where surfaces are frequently painted or coated. Even small amounts of a silicone deposit are sufficient to impair paint adhesion.